1. Technical Field
The present invention relates to a magnetic transfer method and magnetic transfer device that transfer preformatted information to a magnetic recording medium using a master disk having a ferromagnetic material pattern corresponding to preformatted signals.
2. Related Art
In a general hard disk drive device, a magnetic head is caused to fly around 10 nm above a magnetic recording medium, and a data read/write is carried out. Bit information on the magnetic recording medium is stored in concentrically disposed data tracks. The magnetic head is positioned above the data tracks when reading or writing data. Servo information for the positioning is recorded concentrically with the data tracks at constant angle intervals on the magnetic recording medium. As preformatted signals including this kind of servo information are generally recorded using the magnetic head, a problem has occurred in that a write time has increased along with an increase in recording tracks in recent years, and the production efficiency of the magnetic recording medium has dropped. For this reason, a method has been proposed whereby, instead of writing the preformatted signals using the magnetic head, the preformatted signals are recorded en bloc on the magnetic transfer medium by means of a magnetic transfer technique, using a master disk on which the preformatted signals are recorded. For example, a method is known whereby, using a master disk on which is formed a ferromagnetic material pattern corresponding to the preformatted signals, the preformatted signals of the master disk are transferred to a perpendicular recording medium (for example, refer to JP-A-2002-083421).
Herein, referring to FIG. 21, a description will be given of the principal of a magnetic transfer from a master disk to a medium to be transferred. An convex-concave pattern 105 formed from a ferromagnetic material is provided on a transfer master disk 101, and brought into close contact with a medium to be transferred 102. On applying an external magnetic field 106 in a direction parallel to a recording surface of the medium to be transferred 102, a leakage flux 107 enters into the medium to be transferred 102 side. Because of this, a magnetic layer 108 of the medium to be transferred 102 is magnetized (magnetizing directions are shown by arrows 109 in the diagram), and magnetic signals are transferred to the medium to be transferred 102 following the ferromagnetic material pattern 105 of the master disk 101. This kind of method is called an edge transfer method. One pair of magnets 103 disposed above and below the master disk 101 and medium to be transferred 102 rotate simultaneously, and the transfer is made to the whole of the medium to be transferred 102 at one time.
As another magnetic transfer method, there is also a method called a bit transfer. Referring to FIGS. 22A and 22B, a description will be given of a magnetic transfer method using the bit transfer method. Firstly, as shown in FIG. 22A, a first magnetic field 111 is applied in an approximately perpendicular direction to a surface of the medium to be transferred 102 using the one pair of magnets 103, magnetizing the medium to be transferred 102 in one direction. Next, as shown in FIG. 22B, the transfer master disk 101 and medium to be transferred 102 are brought into close contact, and a second magnetic field 113 of an orientation opposite to that of the first magnetic field 111 is applied using the one pair of magnets 103.
Only a small amount of a magnetic flux 115 passes through the depressed portions of the ferromagnetic pattern formed on the master disk 101, and the orientation of the magnetization with the first magnetic field 111 remains. As a large amount of the magnetic flux 115 can pass through the projecting portions of the ferromagnetic pattern, they are magnetized with the orientation of the second magnetic field 113. As a result of this, a magnetization pattern corresponding to the convex-concave pattern formed on the surface of the master disk 101 is transferred to the medium to be transferred 102.
With the heretofore described kinds of transfer magnetic field, after causing the magnets to rotate and transferring a predetermined pattern, it is necessary to cause the magnets to separate from the master disk and medium to be transferred. In the event of stopping the rotation of the magnets when causing them to separate, the magnetic field becomes uneven at a withdrawal position of the magnets, causing a signal deterioration. In order to prevent this kind of signal deterioration, a method has been proposed whereby the deterioration of the transfer signal at the withdrawal position is prevented by causing the magnets to separate from the master disk and medium to be transferred while maintaining their rotation (for example, refer to Japanese Patent No. 3,396,476).
Meanwhile, when considering a magnetic transfer to a magnetic recording medium with the high coercivity of recent years, there is a tendency for the magnetic field needed for the magnetic transfer to become larger. Also, with the kind of method disclosed in Japanese Patent No. 3,396,476, the magnets need a length that covers the inner periphery to the outer periphery of a region of the medium to which the transfer is to be made, an attractive force between the magnets disposed above and below the medium to be transferred in the case of the bit transfer, and a repulsive force between the magnets in the case of the edge transfer, increases, and it is necessary to increase the rigidity of a magnet holding portion in the transfer device. This leads to an increase in size of the transfer device. Furthermore, it is difficult to fabricate magnets of that kind of size evenly over the whole surface.
Also, with the kind of magnetic field application method disclosed in Japanese Patent No. 3,396,476, as a total of at least two rotations—one rotation for the application of the transfer magnetic field and one rotation for the separation of the magnets and medium to be transferred—are necessary, there is also room for improvement from the point of view of shortening the processing time.